What are the guidelines for managing Fetal Growth Restriction (FGR)?

Guidelines for Managing Fetal Growth Restriction (FGR)

The Society for Maternal-Fetal Medicine (SMFM) 2020 Consult Series #52 provides the most comprehensive and authoritative framework for FGR management, emphasizing a structured approach based on gestational age at diagnosis, severity of growth restriction, and umbilical artery Doppler findings. 1

Definition and Diagnosis

• FGR is defined as an estimated fetal weight (EFW) or abdominal circumference (AC) below the 10th percentile for gestational age using population-based references such as Hadlock curves. 1, 2
• Severe FGR is specifically defined as EFW less than the 3rd percentile. 1, 2
• FGR is classified by timing: early-onset FGR occurs at less than 32 weeks gestation, while late-onset FGR occurs at 32 weeks or beyond. 1, 2

Initial Workup and Diagnostic Testing

• For early-onset FGR (less than 32 weeks), perform a detailed anatomical ultrasound examination because up to 20% of cases are associated with fetal structural or chromosomal abnormalities. 1, 2
• Offer chromosomal microarray analysis (CMA) when unexplained isolated FGR is diagnosed before 32 weeks of gestation, as CMA provides a 4-10% incremental yield over standard karyotyping. 1, 2
• If FGR is accompanied by fetal malformations or polyhydramnios at any gestational age, offer prenatal diagnostic testing with CMA regardless of timing. 2, 3
• Consider PCR testing for cytomegalovirus (CMV) in women with unexplained FGR who undergo amniocentesis. 2

Surveillance Protocol Based on Severity

For FGR with EFW 3rd-9th Percentile (Moderate FGR)

• Perform umbilical artery Doppler every 1-2 weeks initially for the first 1-2 weeks after diagnosis to detect rapid deterioration. 1, 2
• If umbilical artery Doppler remains stable and normal after initial assessment, extend the interval to every 2-4 weeks. 1, 2
• Perform cardiotocography (CTG/NST) once weekly after viability. 1, 2
• Reassess fetal growth every 3-4 weeks, though consider 2-week intervals in borderline cases. 1

For Severe FGR (EFW Less Than 3rd Percentile)

• Perform umbilical artery Doppler weekly to monitor for progression to absent or reversed end-diastolic velocity. 1, 2
• Perform cardiotocography once weekly. 1
• Consider reassessing fetal growth every 2 weeks given the higher risk profile. 1

For FGR with Absent End-Diastolic Velocity (AEDV)

• Increase umbilical artery Doppler assessment to 2-3 times per week due to potential for rapid deterioration to reversed end-diastolic velocity. 1, 2
• Increase cardiotocography frequency based on clinical scenario and other comorbidities. 2
• Consider hospitalization if fetal surveillance more than 3 times per week is necessary. 1

For FGR with Reversed End-Diastolic Velocity (REDV)

• Hospitalize immediately, administer antenatal corticosteroids, and perform cardiotocography at least 1-2 times daily. 1, 2
• Strongly consider delivery depending on gestational age and the complete clinical picture. 1, 2

Timing of Delivery

The timing of delivery is determined by the severity of FGR and umbilical artery Doppler findings, not by cerebroplacental ratio alone:

• For FGR with EFW 3rd-10th percentile and normal umbilical artery Doppler: deliver at 38-39 weeks gestation. 2, 3, 4
• For severe FGR (EFW less than 3rd percentile) or FGR with decreased diastolic flow (but without AEDV/REDV): deliver at 37 weeks gestation. 2, 3, 4
• For FGR with absent end-diastolic velocity (AEDV): deliver at 33-34 weeks gestation. 2, 4
• For FGR with reversed end-diastolic velocity (REDV): deliver at 30-32 weeks gestation. 2, 4

Mode of Delivery

• For pregnancies with FGR complicated by AEDV or REDV, strongly consider cesarean delivery based on the entire clinical scenario, as these fetuses have limited physiologic reserve to tolerate labor. 2, 3, 4
• For FGR with preserved end-diastolic flow, vaginal delivery with continuous electronic fetal monitoring is appropriate. 4
• Continuous fetal heart rate monitoring during labor is mandatory for all FGR cases regardless of delivery mode. 2

Antenatal Interventions

• Administer antenatal corticosteroids if delivery is anticipated before 33 6/7 weeks gestation, or for pregnancies between 34 0/7 and 36 6/7 weeks in women at risk of preterm delivery within 7 days. 2, 3
• Administer intrapartum magnesium sulfate for fetal neuroprotection in pregnancies less than 32 weeks gestation. 2
• Low-dose aspirin (81-160 mg daily, taken in the evening) is recommended for women at increased risk of preeclampsia, which may also reduce FGR risk. 2

Critical Pitfalls to Avoid

• Do not delay delivery beyond the recommended gestational age thresholds even with reassuring testing, as stillbirth risk increases with expectant management beyond these timepoints. 4
• Do not rely solely on cerebroplacental ratio to guide delivery timing, as current evidence shows variable sensitivity and specificity, and guidelines do not support this practice. 4
• Do not miss the progression from decreased end-diastolic velocity to AEDV or REDV, which requires immediate escalation of surveillance and earlier delivery. 1, 4
• Do not use birthweight curves for identifying FGR at early gestational ages; use in utero growth curves that represent physiological growth more accurately. 2
• Hospital admission should be considered when fetal surveillance more frequently than 3 times per week becomes necessary. 1

Special Considerations

• Maternal hypertensive disease is present in 50-70% of early-onset FGR cases and is associated with poorer outcomes including earlier delivery and lower birthweights. 2
• The single most important prognostic factor in preterm FGR is gestational age at delivery, with a 1-2% increase in intact survival for every additional day in utero up to 32 weeks gestation. 2
• Placental histopathological examination should be performed after delivery to identify underlying pathology. 5